Apart from the Big Bang Theory, the two theories which captured the attention of cosmologists and drew a number of supporters are:
The Pulsating Theory: This theory is a cosmological model originally proposed by Alexander Friedman in 1922. According to this theory, the universe alternately expands and contracts i.e. the universe undergoes a series of oscillations, each beginning with a big bang and ending with a big crunch. This model proposes an inner and outer limit for the universe. The universe expands for a while after the big bang until it reaches the outer limit, after which the gravitational attraction of matter causes it to collapse back in.
However, many scientists argue that the Pulsating model of the universe fails to satisfactorily explain a number of cosmological phenomena. Also observations and measurements suggested that the universe is not closed. All these have caused most cosmologists to abandon this Pulsating Universe model.
The Steady State Theory: The Steady State Theory is a model developed by Hermann Bondi, Thomas Gold, and Fred Hoyle in 1948. According to this theory, new matter is continuously created out of nowhere as the universe expands, so that the steady state of the universe is perfectly maintained. Though it violates the fundamental law of energy conservation, it had a many supporters in the 1960s.
The number of supporters decreased considerably with the discovery of Cosmic Microwave Background Radiation. Also observations showed that the universe is in fact changing. Quasars and Radio Galaxies are found only at large distances, not in closer galaxies. This means that they existed only in the distant past.
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